A single-storey extension adds ground-floor space to your house, usually at the back or side, built on new foundations with its own walls and roof. Most are used to create a larger kitchen-diner, a family room or a utility and WC. Many fall within permitted development, so planning permission isn't always needed, but Building Regulations approval always is.
If your kitchen feels cramped, or the family has outgrown the downstairs rooms, a single-storey extension is often the simplest way to gain space without moving. A typical rear extension adds 3–4 metres of depth across the back of a semi or terrace, opening the existing kitchen into a bright kitchen-diner with roof lights and wide glazed doors onto the garden. Side extensions suit homes with a gap or driveway beside the house.
It suits households planning to stay put for a while, because the money goes into the house rather than into stamp duty and moving costs. The work happens mostly outside until the final few weeks, when we break through into the existing house, so most families live at home throughout. We arrange the drawings, structural calculations and Building Regulations approval, and we'll tell you early whether your design is likely to need a planning application.
Which options suit your home?
Rear kitchen-diner extension
The usual layout: a 3–6 metre extension across all or part of the back wall, with the old rear wall replaced by a steel beam so the new and existing rooms become one space. Roof lights or a lantern bring daylight into the middle of the house, and bifold or sliding doors open onto the garden.
Side or side-return extension
Uses the strip of land beside the house, often a passage or driveway. Under permitted development a side extension can be up to half the width of the original house and no more than 4 metres high. On a terrace with a narrow side return, it can widen a galley kitchen considerably without eating into the garden.
Wrap-around extension
Combines a side and rear extension into an L shape, giving the largest ground-floor gain. Because it extends both sideways and rearwards, a wrap-around normally needs a householder planning application rather than relying on permitted development. Expect more steelwork and a more involved roof where the two sections meet.
Flat roof or pitched roof
Flat roofs, usually GRP fibreglass or EPDM rubber, keep the height down near boundaries and suit roof lanterns. Pitched or lean-to roofs with tiles to match the house look more traditional and shed rain faster, but need more height. The choice affects permitted development limits, cost, and how much light reaches the existing rooms.
Utility, WC or boot-room extension
A smaller extension of 6–12 m² can take the washing machine, coats and a downstairs toilet out of the kitchen. Adding a WC means a new waste connection, so the position of the existing drains often decides the layout. It's a cost-effective way to free up the main rooms without a large build.
What's included when SKJ does the work?
- Free home survey, measurements and a written, itemised quote
- Drawings arranged for planning and Building Regulations, plus structural calculations for foundations and steels
- Building control application, site inspections and the completion certificate at the end
- Party wall notices drafted where the work is on or near a shared boundary, ready for you to serve
- Groundworks, foundations, drainage alterations and the full shell: walls, roof, windows and doors
- Steel beam and making good where the extension opens into the existing house
- Electrics, heating, insulation and plastering to a finish ready for decorating
- Skip hire, waste removal and a swept, tidy site at handover
How much does a single-storey extension cost?
Guide prices run from £28,000 to £90,000 depending on size and specification. A 4 m × 5 m rear extension on a semi, with roof lights and bifold doors: typically £40,000 – £52,000.
| Option | Guide price | Good to know |
|---|---|---|
| Small rear or side extension (10–15 m²) | £28,000 – £40,000 | Utility, WC or a modest kitchen extension |
| Rear kitchen-diner extension (18–25 m²) | £38,000 – £58,000 | The glazing spec moves it within the range |
| Wrap-around or large extension (30 m²+) | £58,000 – £90,000 | More steel and roof, and normally a planning application |
Usually included: Drawings, structural calculations, building control fees, foundations, shell, roof, windows and doors, steel beam, electrics, heating, insulation and plastering to a finish ready for decorating.
Usually extra: Council planning or certificate fees, party wall surveyor fees if a neighbour dissents, kitchen units and appliances, flooring and decorating.
Guide ranges are the total a homeowner would expect to pay, including VAT where it applies. Your fixed price comes after a free survey.
What changes the price?
- Size and shape: a simple rectangle costs less per m² than an L-shape or wrap-around
- Glazing: wide bifold or sliding doors and roof lanterns are among the biggest single costs
- Ground conditions, nearby trees and drains, which can mean deeper foundations or a build-over application
- How much steel is needed to open up the back of the house
- Roof type, as a flat roof usually costs less than a pitched, tiled one
- Access to the back garden, because tight access means moving materials by hand
How does the job run, start to finish?
- Free survey and measureWe visit, measure the house and garden, look at drains, boundaries and access, and talk through how you want the space to work. You get a written, itemised quote with the payment stages set out, and an honest view on whether planning permission is likely.
- Drawings and approvalsDrawings and structural calculations are prepared, then submitted for a lawful development certificate, prior approval or a planning application as needed, alongside Building Regulations. Party wall notices go out at this stage if they're required, because the notice periods have to run before work can start.
- Groundworks and foundationsThe extension is set out, foundations are dug and building control inspects them before concrete goes in. Any drains in the way are diverted or protected. This is the messiest stage, and access to the back garden matters, so we agree a route for barrows and skips before we start.
- Shell, roof and windowsWalls go up to roof height, the roof is formed, insulated and covered, and windows and doors are fitted so the extension is weathertight. Until this point your existing house stays closed off from the work, and daily life carries on much as normal inside.
- Break-through and first fixThe steel beam is installed and the old rear wall is opened up. Electricians and plumbers run cables, radiator pipes and any waste pipes before the walls and ceilings are insulated, boarded and plastered. This is the stage when the kitchen is most likely to be out of use.
- Second fix, sign-off and handoverSockets, lights, radiators and skirting go in, and floors are screeded ready for your flooring. Building control carries out the final inspection. You walk round with us to check everything before the final payment, and you keep the completion certificate for your records.
Timescale: Usually 8–12 weeks on site once approvals are in place.
Planning, Building Regulations and approvals
Do I need planning permission for a single-storey extension?
Often not. Under permitted development a rear extension can project up to 3 metres from the original back wall of a semi or terrace, or 4 metres for a detached house, and be no more than 4 metres high. Through the prior approval route, where the council consults neighbours, those depths rise to 6 and 8 metres. Within 2 metres of a boundary the eaves can't exceed 3 metres, and extensions and outbuildings together can't cover more than half the land around the original house. Flats, conservation areas and homes with restrictive conditions or Article 4 directions follow different rules.
Which Building Regulations apply to an extension?
Every extension needs Building Regulations approval, through either a full plans application or a building notice. The main parts are A (structure and foundations), B (fire safety), F (ventilation), H (drainage), L (energy efficiency) and P (electrical safety). Under Part L, new walls and floors need U-values of 0.18 W/m²K or better and new roofs 0.15. If glazing exceeds 25% of the extension's floor area, plus the area of any windows or doors it covers up, extra energy calculations are needed. Building control inspects at key stages and issues a completion certificate.
Does the Party Wall Act affect my extension?
It can. Under the Party Wall etc. Act 1996 you must give a neighbour at least one month's written notice before building a new wall on or up to the boundary line, or before digging foundations within 3 metres of their building that go deeper than theirs (6 metres for some deeper excavations). Work to an existing party wall needs two months' notice. For excavation and party wall notices, no reply within 14 days means a dispute has arisen, and surveyors agree an award, usually at the building owner's cost.
What if there's a public sewer under my garden?
If you plan to build over or close to a public sewer, the sewerage company must agree before work starts; across most of the West Midlands that is Severn Trent. A simple domestic extension over a small pipe can often use a self-certification route, while larger pipes, manholes or certain foundation types need a formal build-over agreement. Planning permission and Building Regulations approval don't cover this, so we check sewer records at the survey stage.
Single-storey extensions: your questions answered
How much does a single-storey extension cost in the West Midlands?
Most single-storey extensions in the West Midlands cost between £28,000 and £90,000, including VAT where it applies. A typical 4 m × 5 m rear kitchen-diner on a semi, with roof lights and bifold doors, usually costs £40,000–£52,000 built to a finish ready for decorating. Kitchen units, flooring and decorating are extra. After the free survey you get a fixed price for the agreed specification.
How long does a single-storey extension take?
Allow 8–12 weeks on site for most single-storey extensions, plus time beforehand for drawings and approvals. If you need a planning application or a lawful development certificate, councils aim to decide within 8 weeks. Glazing and steel are ordered early so they arrive when the shell is ready, which keeps the build from stalling halfway.
Can we live at home during the build?
Yes, most families stay at home throughout. For the first several weeks the work is outside and your house is closed off from it. The disruptive part is the break-through, when the back wall comes out and the kitchen may be out of action for one to three weeks. We agree a plan for a temporary sink and cooking space before that stage starts.
Do I need to tell my neighbours about an extension?
You don't need their permission for permitted development, but you will usually need to involve them. Under the prior approval route the council writes to adjoining neighbours and gives them 21 days to comment. If the build is on the boundary or the foundations are deep and close to their house, the Party Wall Act requires formal written notice. A friendly conversation before any notice arrives usually makes everything smoother.
What guarantees come with the extension?
Windows, doors, roof lights and roofing membranes come with manufacturers' guarantees, and the terms for each product are set out in your quote. Building control's completion certificate confirms the work met Building Regulations when inspected. If anything in our workmanship isn't right after handover, call us and we'll come back and look at it. Ask us for current insurance details with your quote.
What should I prepare before the survey?
Think about how you want to use the new space, and gather anything you have about the house: old plans, deeds showing boundaries, approvals for any earlier extension, and where you think the drains run. Photos of extensions you like help us price glazing and finishes accurately. If you're in a conservation area or on a newer estate, mention it, as it can affect permitted development.
Which areas do we cover for single-storey extensions?
We cover the whole West Midlands from West Bromwich. Pick your area for local details, councils and postcodes:
- Single-storey extensions in Sandwell
- Single-storey extensions in Birmingham
- Single-storey extensions in Dudley
- Single-storey extensions in Walsall
- Single-storey extensions in Wolverhampton
- Single-storey extensions in Solihull
- Single-storey extensions in Coventry
- Single-storey extensions in Staffordshire
- Single-storey extensions in Worcestershire
- Single-storey extensions in Warwickshire